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Date: Thu, 28 May 2015 18:07:52 -0700 From: Andy Lutomirski <luto@...capital.net> To: Gu Zheng <guz.fnst@...fujitsu.com> Cc: "H. Peter Anvin" <hpa@...or.com>, Andy Lutomirski <luto@...nel.org>, Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>, Thomas Gleixner <tglx@...utronix.de>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org> Subject: Re: [RFC PATCH] x86, espfix: postpone the initialization of espfix stack for AP On Wed, May 27, 2015 at 6:20 PM, Gu Zheng <guz.fnst@...fujitsu.com> wrote: > ping... > > On 05/22/2015 06:13 PM, Gu Zheng wrote: > >> The following lockdep warning occurs when running with 4.1.0-rc3: >> [ 3.178000] ------------[ cut here ]------------ >> [ 3.183000] WARNING: CPU: 128 PID: 0 at kernel/locking/lockdep.c:2755 lockdep_trace_alloc+0xdd/0xe0() >> [ 3.193000] DEBUG_LOCKS_WARN_ON(irqs_disabled_flags(flags)) >> [ 3.199000] Modules linked in: >> >> [ 3.203000] CPU: 128 PID: 0 Comm: swapper/128 Not tainted 4.1.0-rc3 #70 >> [ 3.221000] 0000000000000000 2d6601fb3e6d4e4c ffff88086fd5fc38 ffffffff81773f0a >> [ 3.230000] 0000000000000000 ffff88086fd5fc90 ffff88086fd5fc78 ffffffff8108c85a >> [ 3.238000] ffff88086fd60000 0000000000000092 ffff88086fd60000 00000000000000d0 >> [ 3.246000] Call Trace: >> [ 3.249000] [<ffffffff81773f0a>] dump_stack+0x4c/0x65 >> [ 3.255000] [<ffffffff8108c85a>] warn_slowpath_common+0x8a/0xc0 >> [ 3.261000] [<ffffffff8108c8e5>] warn_slowpath_fmt+0x55/0x70 >> [ 3.268000] [<ffffffff810ee24d>] lockdep_trace_alloc+0xdd/0xe0 >> [ 3.274000] [<ffffffff811cda0d>] __alloc_pages_nodemask+0xad/0xca0 >> [ 3.281000] [<ffffffff810ec7ad>] ? __lock_acquire+0xf6d/0x1560 >> [ 3.288000] [<ffffffff81219c8a>] alloc_page_interleave+0x3a/0x90 >> [ 3.295000] [<ffffffff8121b32d>] alloc_pages_current+0x17d/0x1a0 >> [ 3.301000] [<ffffffff811c869e>] ? __get_free_pages+0xe/0x50 >> [ 3.308000] [<ffffffff811c869e>] __get_free_pages+0xe/0x50 >> [ 3.314000] [<ffffffff8102640b>] init_espfix_ap+0x17b/0x320 >> [ 3.320000] [<ffffffff8105c691>] start_secondary+0xf1/0x1f0 >> [ 3.327000] ---[ end trace 1b3327d9d6a1d62c ]--- >> >> This seems a mis-warning by lockdep, as we alloc pages with GFP_KERNEL in >> init_espfix_ap() which is called before enabled local irq, and the lockdep >> sub-system considers this behaviour as allocating memory with GFP_FS with >> local irq disabled, then trigger the warning as mentioned about. >> >> Though we could allocate them on the boot CPU side and hand them over to >> the secondary CPU, but it seems a waste if some of cpus are still offline. >> As there is no need to these pages(espfix stack) until we try to run user >> code, so we can postpone the initialization of espfix stack after cpu >> booted to avoid the noise. Does this pass the sigreturn_32 test on both 32-bit and 64-bit kernels and sigreturn_64 test on 64-bit kernels? (The test is in tools/testing/selftests/x86.) If so, looks good to me. --Andy >> >> Signed-off-by: Gu Zheng <guz.fnst@...fujitsu.com> >> --- >> arch/x86/kernel/smpboot.c | 14 +++++++------- >> 1 file changed, 7 insertions(+), 7 deletions(-) >> >> diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c >> index 50e547e..3ce05de 100644 >> --- a/arch/x86/kernel/smpboot.c >> +++ b/arch/x86/kernel/smpboot.c >> @@ -240,13 +240,6 @@ static void notrace start_secondary(void *unused) >> check_tsc_sync_target(); >> >> /* >> - * Enable the espfix hack for this CPU >> - */ >> -#ifdef CONFIG_X86_ESPFIX64 >> - init_espfix_ap(); >> -#endif >> - >> - /* >> * We need to hold vector_lock so there the set of online cpus >> * does not change while we are assigning vectors to cpus. Holding >> * this lock ensures we don't half assign or remove an irq from a cpu. >> @@ -901,6 +894,13 @@ static int do_boot_cpu(int apicid, int cpu, struct task_struct *idle) >> } >> } >> >> + /* >> + * Enable the espfix hack for this CPU >> + */ >> +#ifdef CONFIG_X86_ESPFIX64 >> + init_espfix_ap(); >> +#endif >> + >> /* mark "stuck" area as not stuck */ >> *trampoline_status = 0; >> > > -- Andy Lutomirski AMA Capital Management, LLC -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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